In recent years, in order to achieve high breakdown voltage, low loss, and utilization under a high temperature environment of semiconductor devices such as a Schottky barrier diode (hereafter referred to as an SBD), silicon carbide has begun to be adopted as a material for a semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap larger than that of silicon, which has been conventionally widely used as a material for semiconductor devices. Hence, by adopting silicon carbide as a material for a semiconductor device, the semiconductor device can have a high breakdown voltage, reduced on-resistance, and the like. Further, the semiconductor device thus adopting silicon carbide as its material has characteristics less deteriorated even under a high temperature environment than those of a semiconductor device adopting silicon as its material, advantageously.
For example, Japanese Patent Laying-Open No. 3-185870 (PTD 1) describes an SBD made of silicon, having an insulating film with a taper formed on an n type layer, and an electrode film in contact with the taper portion and the n type layer. Japanese Patent Laying-Open No. 3-185870 also describes that, when the insulating film is formed to be tapered, it is easy to alleviate an electric field, but it is difficult to obtain a high breakdown voltage.
Further, Japanese Patent Laying-Open No. 2-151067 (PTD 2) discloses a junction barrier Schottky diode (hereafter referred to as a JBS) made of silicon, having PN junctions selectively provided in contact with a barrier metal. The JBS is formed to prevent depletion layers formed by adjacent PN junctions from coupling with each other and interrupting a forward current at the time of forward bias, and is configured such that the depletion layers formed by the adjacent PN junctions couple with each other and interrupt a reverse leakage current at the time of reverse bias.
Furthermore, Japanese Patent Laying-Open No. 2003-101039 (PTD 3) describes an SBD made of silicon carbide, having an insulating film, an electrode, a field plate which is in contact with a surface of the insulating film and is electrically connected with the electrode, an edge termination layer, a RESURF layer, and a guard ring layer. Japanese Patent Laying-Open No. 2003-101039 describes that, by forming the guard ring layer having a low impurity concentration comparable to that of the RESURF layer around the RESURF layer, the guard ring can serve to suppress a reduction in breakdown voltage when the impurity concentration of the RESURF layer is higher than an optimum value.